Researchers generate flying qubits in semiconductors

Researchers at Ruhr-Universitat Bochum report the creation of electron qubits in semiconductors. So far, the team says, electron qubits have all been created in a vacuum, so this development really does look like a next step on the oft-mentioned road to quantum computing.

The problem with solid state qubits is, in very broad terms, that electrons are just too friendly. On its path through a material, an electron will interact with that material quite enthusiastically. This means that it cannot maintain a particular state, rendering it unsuitable for use as a qubit.

What the RUB team have done, in collaboration with researchers in Grenoble and Tokyo, is to control the path that an electron will take through a semiconductor.

The work has been published in the March 18 issue of Nature Nanotechnology. It describes how the researcher used high purity gallium arsenide crystal to split an electron on to two paths simultaneously – becoming a so-called flying qubit.

Classically, the electron would either take the upper or the lower path. Quantum mechanically, it can take both at the same time, creating what the researchers have called an alphabet of data processing.

The university announcement explains it as follows: An electron reaches the fork via two closely spaced channels. These are coupled with each other (tunnel-coupling), so that the electron flies simultaneously on two different paths. The phases of the electron waves are maintained by the coupling. The same dual channel was also used by the team after the electron waves were reunited at the end of the fork. In this way, they produced quantum bits with clear states which are suitable for encoding information.

It is early days, however. Professor Andreas Wieck – who came up with the dual channel idea more than two decades ago - commented: "Unfortunately, not all the electrons take part in this process, so far it's only a few per cent. Some students in my department are, however, already working on growing crystals with higher electron densities".